Then you also need a blockstate as usual (blockstates/modelblock.json). Here instead of using another json as a model we directly refer to the obj that is exported from Blender. Because Blender and Forge apparently don't agree on vertical texture coordinate (the 'v' axis) you need to add the 'flip-v' attribute:

The obj file you exported from Blender should go to models/block/model.obj. Note that you also need the model.mtl file which is also exported by blender but you have to modify it so that all referenced textures now use the standard <modid>:<name> format:

Another method of adding textures is through the blockstate file, by adding texture maps. One of the benefits of this is that you can re-export your .mtl file without having to add the map_Kd line each time. Your .mtl file will have at least one "newmtl [name]" line. To map the texture, add "#[name] to the texture map. Instead of the previous example, where you added a "map_Kd" line, you could just change the blockstate to the following: